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Old 04-28-2003, 01:09 AM
Duke2.6 Duke2.6 is offline
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Join Date: Mar 2003
Location: Southern California
Posts: 2,010
Okay, I take it your test was the "two speed no load" test at idle and 2500 RPM.

Does your test report show the amount of O2 in the exhaust? That can add to the story. Your CO2 looks a little low so I would expect to see a few tenths percent 02 if it was measured and written on your test report. Less than 15 percent C02 with a few tenths percent O2 in the exhaust could indicate less than complete combustion and possibly point to the coverters.

I'd like to pursue these M103 emission issues further, and they may apply to all KE system Mercedes engines from the eighties era. The following are test results from my latest California Acceleration Simulatin Mode (ASM) test. This test is done under load on a chassis dynamometer at 15 and 25 MPH, and the load is more than required to maintain a steady speed on a level road, so it simulates acceleration at constant engine speed. My car is a '88 190E 2.6 with a manual transmission, 75K miles. The test is done in second gear for both speeds on this model to maintain the acceptable RPM range. Also, for the last two tests I have been directed to a "test only" station - probably because this engine family has been identified as a high emitter, which is one of the criteria for requiring a test only facility.

Read the data as :

test result/pass limit/average for year group

15 MPH / 1657 RPM

HC: 113/116/31 ppm
CO: 0.36/0.74/0.10 %
NOx: 261/791/237 ppm
O2: 0.1%
CO2: 15.3%

25 MPH / 2665 RPM

HC: 58/91/20 ppm
CO: 0.18/0.62/0.09 %
NOx: 188/199/730
02 0.0%
CO2: 15.3%

The first thing that pops out is the low O2 level. My engine does not have EGR or supplememtal air injection. I believe EGR was added in '89. Does anyone know of any 103 engines with air pumps?

O2 is required to oxidize HC and CO, and on my engine the only sources of O2 are the native exhaust and any reduction of NOx in the three way converter. Once all the O2 is consumed the converter can't do anymore, which is why I think my O2 sensor may have drifted - that is, it is reading less O2 in the exhaust than actually exists, which is causing the system to run slightly rich. The 15+ percent CO2 is an indication of complete combustion.

The '88 maintenance schedule calls for replacement of the O2 sensor once at 60K miles, but I did not do this task. Being as how my CA version has some limited OBD including O2 health and I have never had a check engine light, I decided not to change it, but the OBD is probably not capable of detecting all O2 faults.

The 25 MPH test shows lower HC and CO relative to the standards and year group average and could indicate greater converter efficiency as this test is done immediatly following the 25 MPH test, but the 25 MPH test has a lower relative load. My impression from inspecting other test reports on a wide variety of cars is than the 15 MPH HC is usually the acid test.

I can't draw much in the way of conclusions from the NOx data. Both the test results, limits, and averages have varied widely over the ASM tests that have been done on this and my other cars. It appears that the Califronia Bureau of Automotive Repair is still fiddling with the sampling and software.

The first two emission tests, which were the old two speed no load test showed very low emissions, but they jumped in '95 at 54K miles, so something happened between the '93 and '95.

For those of you who have some expertise in emissions and test analysis, I'd like to hear your remarks.

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